Breast Cancer

What is breast cancer?

Breast cancers are malignanttumors that arise from the uncontrolled growth of cells in the breast. They occur primarily in the ducts that transport milk to the nipple during breast feeding (lactation) and secondarily in the lobules, the glands that produce milk.

Each breast cancer will have its own characteristics. Some are slow-growing; others can be aggressive. Some are sensitive to the hormones estrogen and progesterone, while others can over-express certain proteins. The cancer's characteristics can affect treatment choices and the potential for the cancer to recur.

Each year, more women in the United States are diagnosed with breast cancer than with any other cancer, with the exception of skin cancer. The American Cancer Society (ACS) estimates that 230,480 new cases of invasive breast cancer will be diagnosed in women in the U.S. in 2011 and that about 39,520 women will die from the disease. Men can also develop the disease. ACS estimates that about 2,140 men will be diagnosed with breast cancer in 2011, and about 450 men will die. The rest of this article will focus on breast cancer in women. It is recommended that men who have been diagnosed with breast cancer speak to their doctor for information specific to them and see the ACS's web site All About Breast Cancer in Men.

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This article was last reviewed on November 18, 2011. | This article was last modified on December 29, 2014.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.